1. Field of the Invention
The present invention relates to a use of a tospoviral nucleic acid molecule, particularly to a use of a tospoviral nucleic acid molecule for providing broad-spectrum resistance in transgenic plants against different virus species of the genus Tospovirus. 
2. Description of the Prior Art
Members of the genus Tospovirus are transmitted by thrips in a persistent manner to infect more than 900 species in 82 families of monocots and dicots, and they cause severe damages to many important economic crops around the world. Since thrips species are more abundant in tropical and subtropical areas, more tospovirus species are found in these regions. Due to the high divergence of tospoviruses and the persistent transmission by thrips, so far no significant control strategies are available. Tospoviruses have become economically important plant disease agents in the cultivation of crops all over the world.
A tospovirus has an N (nucleocapsid) gene and an NSm gene. The N gene encodes a tospoviral N (nucleocapsid) protein. The NSm gene encodes a tospoviral nonstructural NSm protein.
A conventional method for generating resistance in tospoviral host plants against tospoviruses has been developed. The conventional method comprises following steps:
(a) Preparing a transgene. The transgene comprises the N gene.
(b) Preparing a transgenic plant by introducing the transgene into a tospoviral host plant.
(c) Allowing the N protein to be expressed in the transgenic plant to produce resistance against tospoviruses.
In an embodiment of the conventional method, the tospoviral host plant used in the conventional method is a tobacco plant. The transgenic plant is a transgenic tobacco plant prepared by introducing a transgene having a tospoviral N gene into a tobacco plant, wherein the N gene is derived from a TSWV isolate. High levels of expressed N protein are accumulated in the transgenic tobacco plants. When challenged with different tospoviral inocula, the transgenic tobacco plants show a broad-spectrum resistance not only against the homologous TSWV isolate but also against heterologous INSV isolates. However, the resistance only provides low levels of protection and can be overcome by increasing inoculum strength.
On the other hand, another conventional method uses a transgenic plant carrying a nontranslatable N gene or NSm gene from a tospovirus. This conventional method triggers RNA-mediated resistance to tospoviruses. The specificity of RNA-mediated resistance appears to be highly protective but functional only against the homologous tospovirus from which the N gene or the NSm gene is originated.
To overcome the shortcomings of the conventional methods, the present invention provides a use of a tospoviral nucleic acid molecule in transgenic plants for conferring high levels of broad-spectrum resistance, including immunity, against different tospovirus species to mitigate or obviate the aforementioned problems.